Sulphuric acid concentration



y 1941- N. TITLESTAD EI'AL 2,249,192

SULPHURIC ACID CONCENTRATION Filed Jan. 31, 1939 l4 CONCENTRAT'O F?DENITRATED H2504 65% AE'RATOR SUPERHEATED STEAM COOLER E :5 i g k iINVENTORS' /V/COA4V 7/72 F3740 BY 4 00/6 /V. fil-Zf/V, MA B Qfimm o MATTORNEY.

Patented July 15, 1941 Nicolay Titlestarl, White Plains, N. Y. and LouisNathan Allen, Jr., Nutley, N. J., assig'nors to Chemical ConstructionCorporation, New York, N. Y., a corporation of Delaware ApplicationJanuary 31, 1939, Serial No. 253,796 I In Great Britain March 18 1938 2Claims. (01. 23-7307) 7 This invention relates to the concentration anddecolorization of denitrated spent sulphuric acid, for example thesulphuric acid remaining after driving off the nitric acid content fromthe spent or waste acid from the manufacture of nitrocellulose or ofnitroglycerine in munitions plants. Such acid, as obtained from thedenitrating towers, is usually of 65-70% concentration and containsappreciable quantities of dark organic compounds which are derived fromthe nitration process.

Heretofore this acid has been concentrated by boiling it in cast ironpots over an open flame to a final concentration of from 93-96%. In thisway the dark organic compounds are broken down and the acid becomes verylight in color, but the process is expensive and wasteful as the potsbreak very frequently and large charges of acid are lost. The fuelconsumption is also extremely high because the heat transfer is limitedto the surface exposed to the flame and the transfer coefiicient is low.

Wehave attempted to concentrate the spent acid by passing hot gasesthrough it which has the advantage of reducing the boiling temperatureof the acid due to the reduced vapor pressure caused by the passage ofthe hot gases. We found, however, that while this method of treatmentwould concentrate the acid satisfactorily, it would not decolorize itbecause this reduced boiling temperature is then toolow. We then foundthat superheated steam, either when used alone or in admixture withother hot gases, will decolorize the dark concentrated acid produced byconcentrating denitrated spent acid to approximately the proper strengtheither by means of hot gases or in a vacuum concentrator or by othermethods in which the concentration is effected at a temperature at orbelow the normal boiling point (i. e. the boiling point underatmospheric pressure) of the acid. Our invention consists, therefore, inconcentrating denitrated spent acid with hot gases or otherwise andthereupon blowing superheated steam into it, either alone or inadmixture with other hot gases. Satisfactory results have been obtainedby the following methods: ,g

(a) Blowing superheated steam into the liquid whereby the steam iscondensed and enters into the acid partly diluting it and raising itstemperature to the boiling point by virtue of the heat evolved duringdilution together with the latent heat of condensation; J

(b) 'Blow'ing superheated steam intothe liquid, condensing the steam andraising the temperature to somewhat below the boiling point, therebydiluting the acid correspondingly.

.(c)' Blowing an excess of superheated steam into the liquid, condensingpart of the steam. The uncondensed part is removed and temperature israised to the boiling point, with corresponding dilution of the acid;

d) Blowing an excess of superheated steam and hot combustion gases intothe liquid, condensing part of the steam. The uncondensed 'part isremoved and the temperature is raised to below the boiling point withoutdiluting the acid.

(6) Blowing an excess of superheatedrsteam into the liquid withoutcondensing any of the steam and raising the acid to the boiling point orslightly below, with or without concentrating the acid further.

A particularly effective method and apparatus constituting a specificfeature of the invention is illustrated in the "accompanying drawing, in

which the single'figure is a diagrammatic illustration of the furnace,concentrators and piping system for'accomplishing the concentration anddecoloriz'ation.

In this drawing the apparatus consists generally of, the combination ofa furnace I, which may be of any known or approvied type, a concentrator2 of the Mast type such as is described in Reissue Patent No. 19,064 anda decolorizer 3 together with an aerator or concentrator 4 forcooling'and further concentrating the decoloriaed acid obtained in thedecolorizer 3.

In the modification shown the furnace l is of the oil or'powdered coalburning type, which is especially well suited for the generation and/orsuperheating of steam and the production of hot gases in accordance withthe present invention. This furnace is equipped with a burner 5 having afuel supply line 6, and an air supply line I, the latter being connectedto an air blower 8. The furnace is divided by a baiile I0 into a firebox '9, which may contain water tubes in the usual manner for generatingsteam, and a dilution chamber ll for diluting the stack gases tosuitable temperatures for use in acid concentration.

In addition to thesteam generating equipment,

which'is not shown, the fire box 9 also contains steam superheatingcoils or tubes which are 11-- lustrated diagrammatically by the steamtube 12, and it is understood that these coils are connected directlywith the steam generating equipment if this is also contained in theboiler. 'on the other hand, steam such as waste steam from any suitableoutside source may be introduced to the coils [2, as through an inletpipe l3, and it is operates.

understood that the invention is not limited in this respect.

As has been stated, the acid concentrator 2 is of a known type, and neednot be described in detail. It consists generally of a plurality ofdrums or concentrating chambers I4 and I5 in which the acid to beconcentrated is passed in countercurrent contact with hot products ofcombustion from the furnace I which are admitted through pipes I6 andI1. nitrated sulphuric acid of about 65% strength is fed to the drum orconcentrating chamber I4 by inlet pipe and is heated and Partiallyconcentrated by the gases entering through the pipe I6 which then leavethrough gas outlet pipe I9. The partially concentrated acid thenoverflows through the outlet 2| into the second drum or concentratingchamber I5 Where it is further concentrated by a second flow of hotgases entering through pipe I'I. Although the acid concentrator is shownas consisting of only two drums or concentrating chambers, it isunderstood that further stages of concentration may be employed ifdesired, the chief requisite being that the acid is finally brought tothe desired concentration, such as 94-96% strength.

The decolo-rizing chamber 3 which in operation constitutes a principalfeature of the invention is preferably similar in form and constructionto one of the concentrating drums or chambers I4 and I5 and is made ofacid-proof material adapted to withstand the high temperatures at whichit In the modification shown it consists of a rectangular or cylindricalchamber provided with a steam inlet pipe 26 extending nearly to thebottom thereof and also preferably provided with an outlet pipe 21 forexcess'steam. A liquid outlet 28 in the form of a pipe or channel islocated at one side of the decolorizing chamber 3 at such a level as to"maintain therein a body of acid of substantial depth, thus retaining theacid within the chamber for a substantial period of time when theapparatus is in continuous operation. The volume of acid so retained inthe chamber 3 is adjusted to the speed of decolorization by thesuperheated steam so that the'acid' is bleached as fast as it isconcentrated in the concentrator 2.

As has been pointed out above the process of our invention may beoperated with or Without a partial condensation of steam and consequentdilution of the acid in the decolorizer 3. In all cases, however, theacid leaving the chamber 25 is very hot and its high heat content may beused for purposes of further concentration by blowing Spent de-" air orother inert gases through it. For the accomplishment of this purpose thedecolorizer 3 is directly connected with an aerator or concentrator 4,which consists of a chamber 30 preferabl similar in shape andconstruction to the chamber 25, but having an air inlet pipe 3|extending below the level of the acid therein. Decolorized acid entersthis chamber through the pipe 28 and is maintained as a body ofsubstantial depth by the location of an outlet pipe 32 which is providedat a suitable elevation in the side wall thereof. Decolorized andconcentrated acid leaving the chamber 30 through this pipe is passedsteam into a hot body of the acid. The necessity for this step arisesfrom the fact that the concentration temperatures in a drum typeconcentrator such as the concentrator 2 are below those at which theorganic colorizing impurities are decomposed or removed. Nitrating acidderived from the manufacture of nitrocellulose or nitroglycerine inmunition plants contains or= ganic impurities of this nature whichremain in the sulphuric acid after it is denitrated and result in a darkcolored product when concentration is accomplished by the use of hotgases alone.

'Spent alcohol acid recovered as a by-product from the production ofsecondary alcohols by the absorption of olefins in sulphuric acid andsubsequent hydrolysis also presents a similar problem, as it containsorganic impurities which darken the acid when it is concentrated at lowtemperatures.

Accordingly, it will be seen that the process of our invention retainsall the advantages accompanying the use of hot gases in concentratingdilute sulphuric acid containing organic impurities and simply adds theadditional decolorizing step of blowing superheated steam into the acid.It is an additional important advantage of the invention that this steamcan be superheated and/or generated in the same equipment that isordinarily used for generating the hot gases used in concentrating, andtherefore the fuel consumptionof the process is not materially altered.In fact, we have found that spent denitrating acid may be concentratedand decolorized to a strength and color suitable for reuse with anexpenditure of fuel only 5% greater than that used in the concentratorsalone. In other words, the

present invention provides light colored acid at a fuel cost of only 5%greater than that required for the production of dark coloredconcentrated acid, and with very little additional capital expenditurefor equipment.

The process of our invention will be illustrated as being carried out inthe apparatus which has been described, but it should be understood thatin its broader aspects it is not limited thereto. On the contrary, it isunderstood that the substitution of alternative and equivalent steps maybe resorted to within the scope of the claims appended hereto. Hotcombustion gases produced in the furnace I by the burning of a fuel suchas 'oil, gas or powdered coal are passed over the super-heating steamcoils I2, and may then be passed over steam generating tubes in theusualmanner if desired. The combustion gases then enter the chamber II wherethey are diluted with air from the blower 8 introduced through thebranch pipe 35 in the air line 3|.

Sufiicient air is added from this source to cool the combustion gases toabout 1100 F., and they pass at this temperature through the pipe I6 andthrough branch pipe I! into the concentrating drums or chambers I4 andI5 where they serve to concentrate spent denitrated sulphuric acid ofabout 65% strength introduced through the feed line 20 in the usualmanner. In a, preferred method of operation the acid in the firstconcentrating drum or chamber I4 is held at -85% strength and the acidin the concentrating drum or chamber- I 5 is heldat 94-96% strength. Thehot gases passing through these bodies-of acid evaporatewater-therefrom, but atternperatures too low to decompose the impuritieswhich they contain. Thus, for example, the acid in chamber. I5 isconcentrated to 94-96% at a temperature of about 440- F., and thereforeleaves this chamber as a dark colored concentrated acid which requiresdecolorization before it is suitable for reuse.

The dark colored acid leaving the concentrator 2 is preferablycontinuously introduced into the decolorizer 3 through a connecting pipe36, at a temperature of 440-450" F. In the decolorizer it is maintainedas a body of substantial depth and volume while steam which has beensuperheated in the coil i 2 to temperatures of about 1000 F. is passedinto it through pipe 26. The temperature of the acid is thereby raisedto about 520-530 FL, partly by taking up sensible heat from the steamand partly by the heat of dilution resulting from condensation of steam.At these temperatures the color forming impurities in the acid arerapidly decomposed. The size of the chamber 25 and the depth of acidtherein are such that the acid is held for a sufficient length of timeto remove substantially all of its colored and color forming impurities,after which it is discharged into the chamber 30 through the pipe 28 asa decolorized acid of 92-93% strength.

As has been pointed out above, it is not always necessary to condense apart of the steam into the acid. On the contrary, an excess ofsuperheated steam may be blown through it without condensing any of thesteam, and the acid is heated to temperatures near its boiling pointsimply by the sensible heat, or superheat, contained in the steam. Inthis way superheated steam at a temperature of 1000-1200" F. or more maybe used to both decolorize and concentrate the acid. It is alsopossible, as is pointed out above, to employ a mixture of superheatedsteam and hot combustion gases in this stage of the process, in whichcase a further concentration of the acid maybe obtained in the chamber25. It will be noted that when a mixture of hot gases and superheatedsteam is used the presence of the steam serves to ofiset the temperaturereducing action of the 30. Acid from the chamber 25 is preferablycontinuously introduced into this chamber through the inlet pipe 28 andair from the blower 8 is passed through it by way of the pipe 3|. Sincethe acid enters at the extremely high temperatures of 5204530? F., itssensible heat content is suflicient to provide the heat necessary forvaporizing its excess content of water, and the acid is thereforeconcentrated by the passage of air through it to a concentration ofabout 93-94%. At the same time, the air stream also serves to cool theacid and to further bleach it by carrying away any volatile coloredimpurities which it may contain. The same result may be accomplished byusing a vacuum evaporator at this details given above, which areprimarily for pur-v poses of illustration.

What we claim is:

1. In a process of decolorizing dilute impure sulphuric acid containingorganic coloringrimpurities in which the diulte acid is heated toconcentrate and decolorize the same, the improve ment which comprises,concentrating the dilute acid to about 94-86% strengthby heating it to'temperatures which are below the normal boiling point, and thereuponblowing superheatedsteam into the hot concentrated acid to raise theacid temperature to about the normalboiling point to decolorize theacid, part of the superheated steam being condensed in and diluting theacid, and thereafter reconcentrating and cooling the hot decolorizedacid by blowing cool air therethrough.

2. In a process of decolorizing dilute impure sulphuric acid containingorganic coloring impurities in which the dilute acid is heated toconcentrate and decolorize the same, the improvement which comprises,concentrating the dilute acid to about 94-96% strength .by theintroduction of hot combustion gases thereinto, and

thereupon blowing super-heated steam into the hot concentrated acid toraise the acid temperature to at least about the normal boiling point todecolorize the acid.

NICOLAY TITLESTAD. IJOUIS NATHAN ALLEN, JR.

